In-place vs. out-of-place training.
 Previous systematizations of Spectre attacks [1]} differentiate
between attacks with in-place and out-of-place training.
In-place attacks are generally simpler to perform, as they rely on repeatedly
executing the victim code itself in order to train a microarchitectural
predictor.
Out-of-place attacks are more powerful, as they allow an attacker to perform
the training step on a branch within the attacker's own code rather than the
victim code.
